As described in application Ser. No. 447,560 (U.S. Pat. No. 3,924,538), earlier mass-transport systems have generally been confined to a rolling vehicle displaceable by electrical or other means along a track or right of way engaged by the vehicle wheels. This system had the advantage that it was capable of carrying substantially unlimited loads, since all of the forces were applied substantially directly via the wheel structures to the supporting surface or rails of the tracks or roadbed.
With greater need for high-speed mass transit, however, such systems have given way to low-friction systems which are not as limited with respect to the speed of the vehicle. For example, electromagnetic-suspension vehicles or magnetic-levitation vehicles have been proposed in which the track is provided with a pair of longitudinally extending magnetically permeable rails while the vehicle is provided with complementary magnetic means so that a magnetic field can close between the vehicle and the track, the forces being transmitted to the latter by the magnetic field spanning the suspension gap.
As described in some of the aforementioned applications, the track can comprise a pair of armature rails each of which is juxtaposed with the electromagnets on the vehicle and a suspension gap is provided between the electromagnet and the armature rails. In the basic system of application Ser. No. 362,012 (U.S. Pat. No. 3,851,594), for example, there is an electromagnetic suspension and guide system for suspended vehicle adapted to switch tracks. The switching of tracks is necessary when the vehicle is to be diverted from a main line onto a spur or branch or is to pass along the main line of the track network across a branch location. A switch arrangement is necessary also when two tracks cross or feed one into the other.
In the arrangement of this latter application, the problem of interruption of the main armature rails at the crossings was solved by providing two sets of rails at the crossing in mutually overlapping relationship in the longitudinal direction. More particularly, the vehicle and track systems comprise a vehicle having two rows of electromagnets on each side, each electromagnet consisting of a U-section core and a coil around its web, each armature rail having a U-configuration so that the shanks of the U define poles which co-operate with the poles of the electromagnets.
A similar system is described in Ser. No. 324,135 (U.S. Pat. No. 3,842,747) such that main and auxiliary rows of electromagnets are provided but each electromagnet consists of a core and an electromagnetic coil wound on this core whereby at least the cores are of such configuration that substantially symmetrical and equivalent magnetic flux paths are adapted to be closed therewith by armature rails approaching the electromagnets selectively from each side, i.e. a main and an auxiliary armature rail which operate alternatively. The vehicles could be driven by linear induction motors as described in application Ser. No. 324,150 filed Jan. 15, 1973 and entitled TWO-SIDED LINEAR INDUCTION MOTORS, ESPECIALLY FOR SUSPENDED VEHICLES (now U.S. Pat. No. 3,820,472).
As pointed out in application Ser. No. 447,560, the problem prior to the development there described was to avoid any intense increase or diminution in the overall magnetic resistance encountered by each longitudinally extending electromagnet arrangement and hence to prevent doubling of the magnetic force which would otherwise be expected because of the simultaneous action of two armature rails and two subrows of electromagnets along each side of the vehicle.
Application Ser. No. 447,560 (U.S. Pat. No. 3,924,538) improved upon the earlier devices by providing a levitation-type vehicle which comprised a pair of transversely spaced longitudinally extending magnet arrangements, each formed from a respective row of electromagnets and lying within the outlines of the vehicle body while depending from the bottom thereof, each of these rows magnetically cooperating with an armature arrangement. The armature arrangement comprised a pair of armature rails selectively co-operating with one or the other subrow of magnets of each main row. The electromagnets had substantially U-section cores to co-operate with the armature rails.
This arrangement allowed the vehicle to pass from a single-beam track to a double-beam track or vice versa. A single-beam track is a central-support structure straddled by the vehicle. A double-beam arrangement is a track structure of the channel type in which the two beams of the track flank the vehicle. Because of the ability of the electromagnets to cooperate either with the central support or single beam structure and the outer support or double-beam structure, the vehicle may pass through cross-overs and onto branch tracks and spurs without difficulty and without requiring movable track members. For example, when one of the outer beams must be interrupted to permit a branching of the vehicle to that side, a central-beam support is provided in this region whereby asymmetric support of the vehicle may be obtained temporarily to permit branching.
Within the cross-overs and branch junctions, the magnetic supporting and guiding function was shifted from an outer subrow of electromagnets to an inner subrow and vice versa several times depending upon the complexity of the switching or crossing function.
Where main rows electromagnets, generally consisting of two subrows, encounter two armature rails simultaneously at such junctions, the magnetic shock or increased magnetic force was of considerable disadvantage and inconvenience unless various techniques were used to provide for nullification of this additional force. The earlier systems to achieve such nullification, described in the aforementioned copending applications, were relatively expensive. They, for example, required flux nullification coils on the various armature rails.
The system described in application Ser. No. 447,560 (U.S. Pat. No. 3,924,538) avoids that problem by providing one of the subrows of the electromagnets of each arrangement as a row of main electromagnets and the other subrow as a row of auxiliary electromagnets and providing the armature rail co-operating with the main electromagnets and the auxiliary electromagnets as main and auxiliary armature rails respectively. The armature rails of the main system can have a pole spacing different from the pole spacing of the armature rails of the auxiliary system so that an encounter between the main armature rail and an auxiliary electromagnet or an auxiliary armature rail and a main electromagnet will not have as effective flux-path closure and hence will be of more limited magnetic affect than would have been the case where the main armature rails are confronted by auxiliary electromagnets of the same pulse speed.
In spite of the expedients described above, it has been found that transport systems with suspended vehicles, which are supported and guided electromagnetically, are prone to interference between the main and auxiliary systems at crossovers, junctions and switches. In a typical system, the track may be provided with a pair of main armature rails extending substantially continuously therealong and the vehicle can have a pair of main electromagnets respectively co-operating with these rails and provided on the outer sides of the vehicle. Along each of the main electromagnets there may be provided a respective row of auxiliary electromagnets so that on each side of the vehicle there is provided an electromagnetic suspension and guiding arrangement. At a branch to the right of a vehicle from the main track, for example, the main electromagnet at the right hand side of the vehicle may remain continuously effective since this limb of the curve is not interrupted and the main armature rail on the right-hand side is continuous. However, since the outer curve side of the vehicle veers away from the continuous main armature rail on the left-hand side, the switch portion must be provided with an auxiliary armature rail which co-operates with the auxiliary electromagnet on the left-hand side to provide temporary support of the vehicle through this portion of the junction. As the auxiliary rail on the outer limb of the curve or the left-hand side of the vehicle approaches the normal straight trace of the right-hand main magnetic arrangement, it must be interrupted and hence beyond this trace, support must be picked up by outer limb auxiliary armature rail coacting with the left-hand auxiliary electromagnets of the vehicle. In the space between these two portions of auxiliary armature rail, there may be provided a stretch of left-hand main armature rail or right-hand main armature rail in a "frog". Where the magnetic axis of the left-hand main electromagnet arrangement and the magnetic axis of the right-hand electromagnet arrangement of the vehicle cross, there is an intersection at which various armature rails approach one another and interfere with the suspension and guiding function.
On passing over a switch portion of the track, all of the supporting and guiding forces for the suspended vehicle on one vehicle side or the other (depending upon whether the vehicle is proceeding into the spur or continues along the main track) are produced alternately by the main magnet system and the auxiliary magnet system. The use of the main magnet system or the auxiliary magnet system is dependent upon the mutual positions of the primary and the secondary part is a necessary condition for producing the required supporting and guidance forces.
The term "primary part" and "secondary part" are used herein to distinguish between the electromagnet (active member) and the armature rail (passive member), it being noted that, in principle, one part or the other can be mounted upon the vehicle and another upon the track. In other words, while the aforementioned applications have generally disclosed systems in which the electromagnet is provided upon the vehicle and the armature rail upon the track and such systems are preferred. It is also conceivable to provide electromagnets along the track which cooperate with armature rails carried by the vehicle.
The parts attached to the track of the main and auxiliary magnet system form a point of intersection at which, for example, two armature rails of the main electromagnet system abut, adjoin or are coterminous with a respective armature rail of the auxiliary electromagnet system and at an obtuse angle.
It has been found that high vehicle speeds, e.g. about 500 km per hour, prevent instantaneous switch-off of one magnet system (e.g. the main magnet system) and simultaneously switch-on of the other magnet system (e.g. the auxiliary magnet system) so that the main electromagnet is only effective in the regions in which it is juxtaposed with the main armature rail and the auxiliary electromagnets are effective only where they are juxtaposed with auxiliary armature rails.
Thus the above mentioned points-of-intersection are traversed by the vehicle with either the main electromagnet energized in the region of the main armature rail, or both on the outside-curve vehicle side.
Accordingly, adjacent the adjoining site (rail-junction region) there occurs an interfering action between the primary part of one magnet system and the secondary part of the other magnet system in addition to the desired suspending and guiding action between the primary and secondary parts of the selected magnet system.
In other words, for example, the electromagnet of the main magnet system on the outer curve side of the vehicle may generate magnetic force by interaction with the auxiliary armature rail of the auxiliary magnet system on this side. These forces create perturbations in the travel of the vehicle and generate discomfort and mechanical shock with its destructive effect upon the structure, and create the need for strengthened supporting structures. Such supporting structures, where they are provided upon the vehicle increase energy consumption and reduce the vehicle payload. With an increase in the distance of the suspended vehicle from the above mentioned point-of-abutment (junction site) the interfering magnetic field decreases because of the rapidly increasing air gap between the primary part of one magnet system and the secondary part of the other.
The mechanical jolts which are applied to the suspended vehicle by the interfering magnetic field in a direction perpendicular to the direction of travel have been found in the past to limit the maximum permitted speed of the vehicle at the switch portion. Furthermore, such vehicles are generally provided with compensating circuitry to provide an electromagnetic counteraction to any perturbations in the path of travel of the vehicle. The speed of response of such corrective equipment must be increased where perturbations are experienced, thereby increasing the cost of the system.